This invention relates generally to turbomachines and, more particularly, to a sealing assembly for use in turbomachines.
Known turbomachines include a defined flow path. For example, at least some known steam turbine engines include at least one of a high pressure (HP) turbine, an intermediate pressure (IP) turbine and/or a low pressure (LP) turbine that, each define a portion of the steam path therein. Known turbomachines also include a rotatable, or rotor shaft extending through such casings. Steam leakage can occur either into or from the steam path, and from areas of higher pressure to areas of lower pressure, wherein such steam leakage is a function of the magnitude of a differential pressure between the two areas. Such leakage may adversely affect the operating efficiency of the turbine. For example, steam-path leakage occurring between the rotor shaft of the turbine and a surrounding turbine casing may reduce the overall efficiency of that turbine. Similarly, steam-path leakage between the rotor shaft and a portion of the casing transiting between adjacent turbine casings may also reduce the overall efficiency of the turbine assembly. Over time, reductions in the operating efficiency of the steam turbine may result in increased fuel costs.
To reduce an amount of flow path leakage, at least some known turbomachines use flow restraining devices, such as seals. Such flow restraining devices generally reduce an overall size of the area that flow can leak through, and thus reduce the amount of steam leakage. For example, labyrinth seals may be positioned between the turbine casings to minimize flow leakage to the atmosphere. At least some known labyrinth seals are formed with a plurality of grooves that circumscribed the rotor shaft. To reduce flow leakage, a clearance between a plurality of stationary seal teeth and the opposing end packing rings is substantially reduced. However, within known turbomachinery, because the flow has a high axial velocity, the flow may “skid” through the grooves and inhibit the effectiveness of such labyrinth seals.